This PDF file contains the front matter associated with SPIE Proceedings Volume 8534, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

In the last decades, atmospheric pollution in urban and industrial areas has become a major concern of both developed and developing countries. In this context, surveying relative large areas in an automatic way is an increasing common objective of public health organisations. The Lidar-Dial techniques are widely recognized as a cost-effective approach to monitor large portions of the atmosphere and, for example, they have been successful applied to the early detection of forest fire. The studies and preliminary results reported in this paper concern the development of an integrated Lidar-Dial system able to detect sudden releases in air of harmful and polluting substances. The propose approach consists of continuous monitoring of the area under surveillance with a Lidar type measurement (by means of a low cost system). Once a significant increase in the density of a pollutant is revealed, the Dial technique is used to identify the released chemicals. In this paper, the specifications of the proposed station are discussed. The most stringent requirement is the need for a very compact system with a range of at least 600-700 m. Of course, the optical wavelengths must be in an absolute eye-safe range for humans. A conceptual design of the entire system is described and the most important characteristic of the main elements are provided. In particular the capability of the envisaged laser sources, Nd:YAG and CO2 lasers, to provide the necessary quality of the measurements is carefully assessed. Since the detection of dangerous substances must be performed in an automatic way, the monitoring station will be equipped with an adequate set of control and communication devices for independent autonomous operation. The results of the first preliminary tests illustrate the potential of the chosen approach.

The instrument set-up designed by the PreViBOSS project for the ParisFog field campaign is suitable to sound microphysical properties of droplets and interstitial aerosols during developed fog in a semi-urban environment. Developed fog is defined as LWC < 7 mg m^-3 and the temperature vertical gradient over 30 m, ΔT, smaller than 0.04 K/m. Visibility averaged over November 2011 is 385±340 m (with rare values larger than 1000 m), and month average of LWC is 60±60 mg m^-3. The droplet effective radius decreases from 14 to 4 μm when the number concentration increases from less than 10 to 220 cm^-3. Particle extinction coefficient is computed by Mie theory applied on size distribution observed during developed fog in ambient conditions by both PALAS WELAS and DMT FM100. Comparison with particle extinction coefficient directly measured by the Degreanne DF20 visibilimeter demonstrates satisfying agreement, within combined uncertainties. Ratio of computed over measured particle extinction coefficient is 1.15±0.35. Visibility smaller than 1000 m at 3 m above ground level is observed not only during developed fog but also during shallow fog, which presents a significant vertical gradient, as ΔT > 0.4 K/m. In this case, LWC is highly variable and may be observed below 7 mg m^-3. The consequent month average of LWC is 30±80 mg m^-3. The optical counters miss large droplets significantly contributing to extinction in shallow fogs. Consequently, it is not possible to reproduce with satisfaction the particle extinction coefficient in shallow fog. Fog type may be distinguished by association of groundbased visibilimeter and MSG/SEVIRI. When clear-sky is given by EUMETSAT/NWCSAF cloud type product while visibility is observed smaller than 1000 m at SIRTA, in 75% cases a shallow fog occurs, and in other cases, horizontal heterogeneity characterises the developed fog within the SIRTA pixel, as during the dissipation phase. Moreover, consistently, low and very low clouds are mostly detected by the satellite product when developed fog is observed by ground-based instrumentation.

We use combined multi-year measurements from the surface and space for assessing the spatial and temporal distribution of aerosol properties within a large (~400x400 km) region centered on Cape Cod, Massachusetts, along the East Coast of the United States. The ground-based Aerosol Robotic Network (AERONET) measurements at Martha’s Vineyard Coastal Observatory (MVCO) site and Moderate Resolution Imaging Spectrometer (MODIS) sensors on board the Terra and Aqua satellites provide horizontal and temporal variations of aerosol optical depth, while the Cloud- Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) offers the altitudes of aerosol-layers. The combined ground-based and satellite measurements indicated several interesting features among which were the large differences in the aerosol properties observed in July and February. We applied the climatology of aerosol properties for designing the Two-Column Aerosol Project (TCAP), which is supported by the U.S. Department of Energy’s (DOE’s) Atmospheric Radiation Measurement (ARM) Program. The TCAP field campaign involves 12-month deployment (started July 1, 2012) of the ground-based ARM Mobile Facility (AMF) and Mobile Aerosol Observing System (MAOS) on Cape Cod and complimentary aerosol observations from two research aircraft: the DOE Gulfstream-1 (G-1) and the National Aeronautics and Space Administration (NASA) B200 King Air. Using results from the coordinated G-1 and B200 flights during the recent (July, 2012) Intensive Observation Period, we demonstrated that the G-1 in situ measurements and B200 active remote sensing can provide complementary information on the temporal and spatial changes of the aerosol properties off the coast of North America.

The mixing layer height (MLH) is an important factor which influences exchange processes of ground level emissions. The continuous knowledge of MLH is supporting the understanding of processes directing air quality. If the MLH is located near to the ground, which occurs mainly during winter and night-time, air pollution can be high due to a strongly limited air mass dilution.

Since 2006 different methods for long-term continuous remote sensing of mixing layer height (MLH) are operated in Augsburg. The Vaisala ceilometers LD40 and CL31 are used which are eye-safe commercial mini-lidar systems. The ceilometer measurements provide information about the range-dependent aerosol concentration; gradient minima within this profile mark the borders of mixed layers. Special software for these ceilometers provides routine retrievals of lower atmosphere layering from vertical profiles of laser backscatter data. The radiosonde data from the station Oberschleissheim near Munich (about 50 km away from Augsburg city) are also used for MLH determination. The profile behavior of relative humidity (strong decrease) and virtual potential temperature (inversion) of the radiosonde agree mostly well with the MLH indication from ceilometer laser backscatter density gradients.

A RASS (Radio-Acoustic Sounding System) from Metek is applied which detects the height of a turbulent layer characterized by high acoustic backscatter intensities due to thermal fluctuations and a high variance of the vertical velocity component as well as the vertical temperature profile from the detection of acoustic signal propagation and thus temperature inversions which mark atmospheric layers. These data of RASS measurements are the input for a software-based determination of MLH. A comparison of the results of the remote sensing methods during simultaneous measurements was performed. The information content of the different remote sensing instruments for MLH in dependence from different weather classes was analyzed further. A special focus is the continuous determination of MLH.

Ceilometers are applied by KIT/IMK-IFU to detect layering of the lower atmosphere continuously. This is necessary because not only wind speed and direction but also atmospheric layering and especially the mixing layer height (MLH) influence exchange processes of ground level emissions. It will be discussed how the ceilometer monitoring information is used to interpret the air pollution near the ground.

The information about atmospheric layering is continuously monitored by uninterrupted remote sensing measurements with the Vaisala ceilometer CL51 which is an eye-safe commercial mini-lidar system. Special software for this ceilometer provides routine retrievals of lower atmosphere layering from vertical profiles of laser backscatter data.

An intensive measurement period during the winter 2011/2012 is studied. The meteorological influences upon air pollutant concentrations are investgated and the correlations of air pollutant concentrations with ceilometer MLH are determined. Benzene was detected by department of Applied Climatology and Landscape Ecology, University of Duisburg-Essen (UDE) with a gas chromatograph during the measurement period. The meteorological data are collected by UDE and the monitoring station Essen of the German national meteorological service DWD. The concentrations of the air pollutants NO, NO₂ and PM₁₀ are provided by the national air pollution network LANUV.

The NDSA (Normalized Differential Spectral Attenuation) approach is based on the conversion of a spectral parameter (the spectral sensitivity S) derived from power measurements, into the total content of water vapor (IWV, Integrated Water Vapor) along the propagation path between the two LEO satellites, through pre-determined IWV-S relations. This paper shows how some problems concerning the relationships between IWV (Integrated Water Vapor) and S could be overcome. In fact, two basic problems affected the reliability of such empirical IWV-S relations found so far: the first was the fact that the accuracy of the radiosonde data used to derive them was not uniformly distributed in the northern and southern hemisphere; the second was the limited amount of radiosonde data available at the highest altitudes (above 10 km), and their scarce reliability. Furthermore, the problem of correcting for the presence of liquid water needed to be considered. Here we present the results of a global scale analysis of the IWV-S relations made utilizing the ECMWF global atmospheric model. S and IWV were simulated and computed at all altitudes from 0 to 20 km, obtaining IWV-S relations for 17, 19, 21, 179 and 182 GHz. Also, the correction of IWV estimates by the presence of liquid water is shown to be effective by using an additional frequency around 30 GHz.

Research indicates that aerosol optical thickness (AOT) values and particulate matter (PM₁₀) measurements can be used as indicators of atmospheric pollution. The problem of relating AOT with suspended particulate matter near the ground is still an open question. While satellite images can provide reliable and synoptic measurements from space, comparisons with monitoring surface level air pollution continues to be a challenge since satellite measurements are column integrated quantities. In this study, in-situ spectroradiometric measurements were taken during satellite overpass using field spectrometers to obtain the reflectance values of the calibration targets used. Sun photometer measurements were taken with the Microtops hand-held sun photometer to measure AOT. Meteorological data was collected from nearby meteorological stations and PM₁₀ measurements were collected from local mobile air pollution stations. Following, the darkest pixel method of atmospheric correction was applied to a series of Landsat satellite images. The reflectance values of the atmospherically-corrected image were used in the radiative transfer equation to solve for AOT. Thematic maps were generated in order to develop air quality indices. The image-derived AOT values were examined for a positive correlation with PM₁₀ measurements. It appears there exists a significant correlation between AOT and PM₁₀ measurements.

This work intends to estimate PM_2.5 concentration over mega city Osaka in Japan based on both satellite and ground measurements. Our work is composed of the following steps. At first the relationship between PM_2.5 and aerosol optical thickness (AOT) is derived by using the ground measurements with sun photometer and PM-sampler, respectively. In addition vertical distribution of aerosol particles are also investigated by LIDAR measurements. The second step is to retrieve columnar AOT distribution from the space-based reflectance information with CAI (cloud aerosol imager) on GOSAT (greenhouse gases observing satellite). Note that, the PM_2.5 measurements indicate the surface level concentration of the atmospheric particles, and hence the columnar AOT distribution should be converted to the surface level aerosol optical depth (AOD) based on the aerosol extinction profile with LIDAR. Finally, PM_2.5 distribution is obtained from the relationship derived at the first step. The obtained results of PM_2.5 are partially validated with the sampling data of PM_2.5 at the surface.

The presence of cirrus clouds introduces complex heating and cooling effects on the atmosphere and can also interfere with remote sensing from satellite-based sensors or from high-altitude aircraft. Detection of cirrus clouds thus provides an opportunity for atmospheric correction to introduce accurate compensation to images of the earth’s surface. Previous work on detection and characterization of cirrus clouds have been based on observing spectral signatures on a spectral channel with significant water absorption, or calculation of radiant intensity ratios over a water band to a reference spectral channel. Our proposed approach is based on applying computational homology to characterize the topological properties of cirrus clouds. We utilize an application called JPLEX to study the persistent homology of multi-dimensional simplicial complexes built from available hyperspectral or multispectral data. The technique has been successfully applied to discriminate subtle features in high dimensional noisy data sets. Previous examples include anomaly detection in hyperspectral images. The analysis makes use of the entire multidimensional data set (not just one or a combination of spectral bands) which may offer advantages in discriminating among various cloud types in a scene, as well as determining other characteristics of cirrus clouds such as altitude and thickness. Our initial computational experiment with an AVIRIS scene has demonstrated that JPLEX is able to discriminate between cumulus and cirrus clouds.

A calculation method has been developed for rapidly synthesizing radiometrically accurate ultraviolet through longwavelengthinfrared spectral imagery of the Earth for arbitrary locations and cloud fields. The method combines cloudfree surface reflectance imagery with cloud radiance images calculated from a first-principles 3-D radiation transport model. The MCScene Monte Carlo code [1-4] is used to build a cloud image library; a data fusion method is incorporated to speed convergence. The surface and cloud images are combined with an upper atmospheric description with the aid of solar and thermal radiation transport equations that account for atmospheric inhomogeneity. The method enables a wide variety of sensor and sun locations, cloud fields, and surfaces to be combined on-the-fly, and provides hyperspectral wavelength resolution with minimal computational effort. The simulations agree very well with much more time-consuming direct Monte Carlo calculations of the same scene.

The Extended-range Atmospheric Emitted Radiance Interferometer (E-AERI) is a moderate resolution (1 cm−1) Fourier transform infrared spectrometer for measuring the absolute downwelling infrared spectral radiance from the atmosphere between 400 and 3000 cm−1. The extended spectral range of the instrument permits monitoring of the 400–550 cm−1 (20–25 μm) region, where much of the infrared surface cooling currently occurs in the dry air of the Arctic. The E-AERI provides information about radiative balance, trace gases, and cloud properties in the Canadian high Arctic. The instrument was installed at the Polar Environment Atmospheric Research Laboratory (PEARL) Ridge Lab at Eureka, Nunavut, in October 2008. Measurements are taken every seven minutes year-round (precipitation permitting), including polar night when the solar-viewing spectrometers are not operated. A similar instrument, the University of Idaho’s Polar AERI (P-AERI), was installed at the Zero-altitude PEARL Auxiliary Laboratory (0PAL), 15 km away from the Ridge Lab, from March 2006 to June 2009. During the period of overlap, these two instruments provided calibrated radiance measurements from two different altitudes. Retrievals of total columns of various trace gases are being evaluated using a prototype version of the retrieval algorithm SFIT2 modified to analyze emission features. In contrast to solar absorption measurements of atmospheric trace gases, which depend on sunlit clear-sky conditions, the use of emission spectra allows measurements year-round (except during precipitation events or when clouds are present). This capability allows the E-AERI to provide temporal coverage throughout the four months of polar night and to measure the radiative budget throughout the entire year. This presentation will describe the new E-AERI instrument, its performance evaluations, and clear sky vs. cloudy measurements.

The determination of the aerosol type in a plume from remotely sensed data without any a priori knowledge is a challenging task. If several methods have already been developed to characterize the aerosols from multi or hyperspectral data, they are not suited for industrial particles, which have specific physical and optical properties, changing quickly and in a complex way with the distance from the source emission. From radiative transfer equations, we have developed an algorithm, based on a Look-Up Table approach, enabling the determination of the type of this kind of particles from hyperspectral data. It consists in the selection of pixels pairs, located at the transitions between two kinds of grounds (or between an illuminated and a shadow area), then in the comparison between normalized estimated Aerosol Optical Thicknesses (AOTs) and pre-calculated AOTs. The application of this algorithm to simulated data leads to encouraging results: the selection of only six pixels pairs allows the algorithm to differentiate aerosols emitted by a metallurgical plant from biomass burning particles, urban aerosols and particles from an oil depot explosion, regardless the size and the aerosol concentration. The algorithm performances are better for a relatively high AOT but the single scattering approximation does not enable the characterization of thick plumes (AOT above 2.0). However, the choice of transitions (type of grounds) does not seem to significantly affect the results.

The airborne Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) is developed to retrieve aerosol microphysical and optical properties from multi-angular and multi-spectral measurements of sky radiance and direct-beam sun transmittance. The necessarily compact design of the 4STAR may cause noticeable apparent enhancement of sky radiance at small scattering angles. We assess the sensitivity of expected 4STAR-based aerosol retrieval to such enhancement by applying the operational AERONET retrieval code and synthetic 4STAR-like data. Also, we assess the sensitivity of the broadband radiative fluxes and the direct aerosol radiative forcing to uncertainties in aerosol retrievals associated with the sky radiance enhancement. Our sensitivity study results suggest that the 4STARbased aerosol retrieval has limitations in obtaining detailed information on particle size distribution and scattering phase function. However, these limitations have small impact on the retrieved bulk optical parameters, such as the asymmetry factor (up to 4%, or ±0.02) and single-scattering albedo (up to 2%, or ±0.02), and the calculated direct aerosol radiative forcing (up to 6%, or 2 Wm^-2).

This paper presents a comparison of the darkest pixel (DP) and empirical line (EL) atmospheric correction methods in order to examine their effectiveness to retrieve aerosol optical thickness (AOT) using the radiative transfer (RT) equations. Research has found that the DP and the EL methods are the two simplest and most effective methods of atmospheric correction; however, which of the two atmospheric correction methods is more effective in deriving accurate AOT values remains an open question. The accuracy of the DP and EL atmospheric correction methods were examined using pseudo-invariant targets in the urban area of Limassol in Cyprus, by using reflectance values before and after atmospheric correction. Eleven Landsat 5 and Landsat 7 satellite images were atmospherically corrected using both the DP and EL methods. The reflectance values following the DP and EL method of atmospheric correction were used in the radiative transfer equation to derive the AOT values. Following, an accuracy assessment was conducted comparing the in-situ AOT values as measured from sun photometers with the AOT values derived from the RT equations in order to determine the effectiveness of the DP and EL methods for retrieving AOT. The study found that the EL atmospheric correction method provided more accurate AOT values than the DP method.

Pseudo-invariant targets are often used for atmospheric correction, as their reflectance values are stable across time. Sand is often used as a pseudo-invariant target, although there is conflicting research about its effectiveness as a pseudo invariant target. This study will examine the effectiveness of volcanic sand as a pseudo-invariant target. The study area is a 250x250 meter area of volcanic beach sand near Limassol, Cyprus. In-situ spectroradiometric measurements were taken using field spectrometers to obtain the reflectance values of volcanic sand over wet and dry conditions. The varying saturation levels of the sand due to rainfall, humidity and high temperatures was considered. A series of Landsat-5 TM and Landsat-7 ETM+ satellite imagery were atmospherically corrected using the darkest pixel method in order to assess the effectiveness of the volcanic sand as a pseudo-invariant target. The mean in-situ in-band reflectance values as found from the ground measurements were compared with the at-satellite reflectance values following atmospheric correction. It was found that precipitation conditions such as rainfall affected the reflectance values of sand. The study found that wet sand had a significantly lower reflectance value compared to dry sand. Further, salinization also affected the reflectance value of volcanic sand. Therefore, precipitation conditions need to be considered when using sand as a non-variant target for atmospheric correction.

Passive Fourier-transform infrared (Passive-FTIR) spectroscopy allows rapidly identification of the air pollution. However, for the localization of a leak and a complete assessment of the situation in the case of the release of a hazardous chemical gas or biological cloud, information about the position and the spatial distribution of a cloud is very important. In this work, a scanning imaging passive FTIR system, which composed of an interferometer, a data acquisition and processing software, a scanning system, a video system, and a laptop has been developed. The concentration retrieval algorithm for the passive FTIR remote measurement of gas cloud is presented, which involves the infrared radiative transfer model, radiometric calibration and absorption coefficient calculation. The concentration of the object gas is retrieved by using the nonlinear least squares method. And no background spectra are required. The remote sensing experiment of SF6 was carried out. The measuring result shows that, the column densities of all directions in which a target compound has been identified may be retrieved by a nonlinear least squares fitting algorithm and algorithm of radiation transfer, a false color image is displayed. The results are visualized by a video image, overlaid by false color concentration distribution image. The system has a high selectivity, and it allows visualization and quantification of pollutant clouds. The system allows mobile, real-time and fast measurements of chemical gas and biological clouds.

Among all the greenhouse gases, methane is the most dynamic and abundant greenhouse gas in the atmosphere. The global concentrations of atmospheric methane has increased more than doubled since pre-industrial times, with a current globally-averaged mixing ratio of ~ 1750 ppbv. Due to its high growth rate, methane brings significant effects on climate and atmospheric chemistry. There has a significant gap for variables between anthropogenic and natural sources and sinks of methane. Satellite observation of methane has been identified that it can provide the precise and accurate data globally, which sensitive to the small regional biases. We present measurements from Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) included on the European environmental satellite ENVISAT, launched on 1st of March 2002. Main objective of this study is to examine the methane distribution over Peninsular Malaysia using SCIAMACHY level-3 data. They are derived from the near-infrared nadir observations of the SCIAMACHY at the University of Bremen through scientific WFM-DOAS retrieval algorithm version 2.0.2.Maps of time averaged (yearly, tri-monthly) methane was generated and analyzed over Peninsular Malaysia for the year 2003 using PCI Geomatica 10.3 image processing software. The maps show dry-air column averaged mixing ratios of methane (denoted XCH4). It was retrieved using the interpolation technique. The concentration changes within boundary layer at all altitude levels are equally sensitive through the SCIAMACHY near-infrared nadir observations. Hence, we can make observation of methane at surface source region. The results successfully identify the area with highest and lowest concentration of methane at Peninsular Malaysia using SCIAMACHY data. Therefore, the study is suitable to examine the distribution of methane at tropical region.

The emergence of high-resolution satellites with new spectral channels and the ability to change its viewing angle has highlighted the importance of modeling the atmospheric effects. So, atmospheric correction serves a critical role in the processing of remotely sensed image data, particularly with respect to identification of pixel content. Efficient and accurate realization of images in units of reflectance, rather than radiance, has proven to be a crucial point in the pre-processing of images in remote sensing applications, acquired under a variety of measurement conditions. However, reflectance of the objects recorded by satellite sensors is generally affected by atmospheric absorption and scattering, sensor-targetillumination geometry, and sensor calibration. These normally result in distortion of the actual reflectance of the objects that subsequently affects the extraction of information from images. The use of atmospheric models has significantly improved the results of the corrections. In this study we have proceeded to make the atmospheric correction of the eight multispectral bands of high resolution WorldView-2 satellite by three different atmospherics models (COST, DOS, 6S) defining the geometry of the satellite observation, viewing angle and setting the weather conditions more suited for the acquired images of the study area (Granadilla, Canary Islands). For this purpose, the reflectance obtained by COST, DOS and 6S atmospheric correction techniques are compared with the Top of Atmosphere (TOA) reflectance. Specifically, the 6S atmospheric correction model, based on radiative transfer theory, provides patterns which describe properly atmospheric conditions in this specific study area for monitoring turbid coastal environments. To check the proper functioning of the atmospheric correction comparison was performed between ground-based measurements and corresponding obtained by the eight multispectral satellite channels through the 6S atmospheric model, with similar date, weather and lighting conditions.

Higashi-Osaka is urban area located on the east of Osaka city in Japan. We equip various ground measurement devices in Higashi-Osaka campus of Kinki University. The data supplied by the Cimel instrument are analyzed with a standard AERONET (Aerosol Robotics Network) processing system. We set up an SPM sampler attached to our AERONET site. It is found from the simultaneous measurements and analyses that clear atmosphere with few small particles is not too often, usually polluted particles from diesel vehicles and industries are suspended at Higashi-Osaka and the characterization of atmospheric particles varies especially in dust phenomenon. Then we performed detailed analysis of atmospheric particles in dust days. We analyzed atmospheric particles with scanning electron microscope coupled with energy dispersive X-ray analyzer. This instrument can detect contain elements of sample by X-ray emanated from the surface of the sample. In order to investigate change of particle properties before and after dust event, we select three cases as before dust reaches to Higashi-Osaka, peak of dust event and after dust event and after dust passes. The results of analyses for each case indicate that nonspherical particles with large particle size are dominant and the main component becomes silicon derived from soil particles at the peak of dust event and soil particles remain after dust event. It is found that sometimes anthropogenic pollutant is transported to Higashi-Osaka before dust comes and components from anthropogenic source increase before dust event.

Aerosol retrieval work from satellite data, i.e. aerosol remote sensing, is divided into three parts as: satellite data analysis, aerosol modeling and multiple light scattering calculation in the atmosphere model which is called radiative transfer simulation. The aerosol model is compiled from the accumulated measurements during more than ten years provided with the world wide aerosol monitoring network (AERONET). The radiative transfer simulations take Rayleigh scattering by molecules and Mie scattering by aerosols in the atmosphere, and reflection by the Earth surface into account. Thus the aerosol properties are estimated by comparing satellite measurements with the numerical values of radiation simulations in the Earth-atmosphere-surface model. It is reasonable to consider that the precise simulation of multiple light-scattering processes is necessary, and needs a long computational time especially in an optically thick atmosphere model. Therefore efficient algorithms for radiative transfer problems are indispensable to retrieve aerosols from space.

Developments in lidar have been driven largely by improvements in two key technologies: lasers and detectors. We describe here a lidar instrument for atmospheric remote sensing using the elastic-backscatter and differential-absorption lidar (DIAL) techniques. The instrument features an all-solid-state laser source combined with a flexible approach to detection providing portability, eye-safe operation and high sensitivity. The system is built around a custom-designed Newtonian telescope with a 0.38 m diameter primary mirror. Laser sources and detectors attach directly to the side of the telescope allowing for flexible customization with a range of equipment. The laser source is based on an optical parametric oscillator (OPO). The OPO is pumped by a neodymiumbased diode-laser pumped solid-state laser and angle-tuned by rotating the nonlinear conversion crystal. This provides a wide range of available wavelengths suitable for lidar within the 1.55 μm to 3.10 μm spectral region, where there exists a relatively high exposure limit for eye safety. The OPO delivers 1 mJ output pulse energy which is expanded and then transmitted coaxially from the telescope. Our goal is to make vertically-resolved measurements of greenhouse gas concentrations using DIAL. The source can rapidly be tuned between the on-line and off-line wavelengths to make a DIAL measurement. The use of the 1.6 μm wavelength region allows for several detection schemes. Whilst photodiode detectors are a very low-cost solution their limited sensitivity restricts the maximum range over which a signal can be detected. We therefore have designed the instrument to support alternative detection schemes including avalanche photodiodes (APDs).

A broadband SWIR/MWIR spectroscopic lidar for detection of gaseous pollutants in air is presented for doing differential optical absorption spectroscopy (DOAS). One of the distinctive parts of the lidar is the use of a picosecond PPMgO:LN OPG (optical parametric generator) capable of generating broadband (10 to <100 nm FWHM) and tunable (1.5 to 3.9 μm) SWIR/MWIR light. The optical source layout and properties are presented, along with a description of the lidar breadboard. Results from indoor simulated typical operation of the lidar will be discussed, the operation consisting in emitting the broadband coherent light along a line of sight (LOS) and measuring the back-scattering returns from of a topographic feature or aerosols. A second distinctive part is the gated MCT-APD focal plane array used in the output plane of the grating spectrograph of the lidar system. The whole of the returned spectra is measured, within a very short time gate, at every pulse and at a resolution of a few tenths to a few nm. Light is collected by a telescope with variable focus for maximum coupling of the return to the spectrograph. Since all wavelengths are emitted and received simultaneously, the atmosphere is “frozen” during the path integrated measurement and hopefully reduces the baseline drift problem encountered in many broadband scanning approaches. The resulting path integrated gas concentrations are retrieved by fitting the molecular absorption features present in the measured spectra. The use of broadband pulses of light and of DOAS fitting procedures make it also possible to measure more than one gas at a time, including interferents. The OPG approach enables the generation of moderate FWHM continua with high spectral energy density and tunable to absorption features of a great number of molecules. Proposed follow-on work and applications will also be presented.

We present the fabrication and characterisation of Dy³⁺-doped tellurite glasses and waveguides for applications in the mid-IR. The low phonon energy and large rare-earth ion solubility of tellurite glasses, as well as having infrared transmission ranges up to <5 μm, make them promising candidates for new mid-IR solid-state laser host materials. This paper presents recent achievements in the fabrication of tellurite glasses, glass characterisation and rare-earth ion spectroscopy which is compared to other glass hosts relevant to the mid-IR such as fluoride glasses. When excited with an 808 nm laser diode source, Dy³⁺ doped tellurite bulk glasses exhibited very broad fluorescence from the ⁶H_13/2 - 6H_15/2 transition which extends from 3 μm to 3.6 μm FWHM compared to 2.9 μm to 3.1 μm in Dy³⁺ doped ZBLAN glass. This broad and red-shifted fluorescence band in tellurite glass may find use in LIDAR and sensing applications as it coincides with an atmospheric transmission band, compared to the ~3 μm emission of Dy³⁺ doped ZBLAN lasers which is absorbed by atmospheric water.

Glyoxal (CHOCHO), as an indicator of photochemical “hot spots”, was for the first time the subject of a differential absorption lidar (DIAL) campaign. The strongest absorption line of glyoxal in the blue wavelength region – 455.1 nm – was chosen as the experimental absorption wavelength. In order to handle the effects of absorption cross-section variation of the interfering gas – nitrogen dioxide (NO₂) – three-wavelength DIAL measurements simultaneously detecting glyoxal and NO₂, were performed. The differential absorption curves, recorded in July 2012, indicate an extremely low glyoxal concentration in Lund, Sweden, although it is expected to be peaking at this time of the year.

Elastic backscatter LIDAR systems have been used to determine aerosol profile concentration in several areas such as weather, pollution and air quality monitoring. In order to determine the aerosol extinction and backscattering profiles, the Klett inversion method is largely used, but this method suffers from lack of information since there are two unknown variables to be determined using only one measured LIDAR signal, and assumption of the LIDAR ratio (the relation between the extinction and backscattering coefficients) is needed. When a Raman LIDAR system is used, the inelastic backscattering signal is affected by aerosol extinction but not by aerosol backscatter, which allows this LIDAR to uniquely determine extinction and backscattering coefficients without any assumptions or any collocated instruments. The MSP-LIDAR system, set-up in a highly dense suburban area in the city of São Paulo, has been upgraded to a Raman LIDAR, and in its actual 6-channel configuration allows it to monitor elastic backscatter at 355 and 532 nm together with nitrogen and water vapor Raman backscatters at 387nm and 608 nm and 408nm and 660 nm, respectively. Thus, the measurements of aerosol backscattering, extinction coefficients and water vapor mixing ratio in the Planetary Boundary Layer (PBL) are becoming available. The system will provide the important meteorological parameters such as Aerosol Optical Depth (AOD) and will be used for the study of aerosol variations in lower troposphere over the city of São Paulo, air quality monitoring and for estimation of humidity impact on the aerosol optical properties, without any a priori assumption. This study will present the first results obtained with this upgraded LIDAR system, demonstrating the high quality of obtained aerosol and water vapor data. For that purpose, we compared the data obtained with the new MSP-Raman LIDAR with a mobile Raman LIDAR collocated at the Center for Lasers and Applications, Nuclear and Energy Research Institute in São Paulo and radiosonde data from Campo de Marte Airport, in São Paulo.

Phosphate glasses can dissolve high concentrations of rare earths and have excellent spectroscopic properties making them useful solid-state laser materials. Solid-state lasers doped with different rare-earth ions find applications in a wide range of LIDAR (Light Detection and Ranging) and sensing applications; phosphate glasses are useful host materials for many applications in the visible and near-infrared spectral regions. For example, trivalent erbium (Er³⁺) doped phosphate glasses operate at the eye-safe wavelength of 1.54 μm and are used for range finding and sensing applications. Tm³⁺ doped solid-state lasers operating at ~ 2 μm can be used for wind-shear and turbulence monitoring. Similarly, Nd-doped metaphosphate glasses are the preferred gain medium for high-peak-power lasers used for fusion energy research because they can store optical energy at greater densities than other glass-types and can be fabricated in large sizes with high rare-earth ion concentration. This paper discusses issues affecting glass quality, with particular focus on defect formation, especially crystallisation. Avoiding crystallisation during processing is essential to form high quality laser cavities. The work presented explores some of the factors controlling these defects including contamination during melting. The crystallisation behaviour of the glass was investigated for several different phosphate glass compositions and different melting conditions, including melting duration, temperature and crucible material.